Bleed duct air systems are used in jet aircraft in order to distribute heat from an airplane engine exhaust for use in other parts of the aircraft. For example, the heat from the engine exhaust may be used to warm a cabin of the aircraft or for more critical aspects of the aircraft. Bleed duct air systems include air ducts that lead from the engine exhaust to various locations within the aircraft. Due to the critical nature of heat transfer in operation of the aircraft, it is necessary monitor the air ducts for leaks, ruptures or other faults. An air duct monitoring system therefore includes one or more sensors placed at various locations along the air duct system. The sensors may be several feet long. These sensors measure a parameter of the air duct system that may be indicative of the state of the air duct (e.g., air duct pressure, air duct temperature) and provide relevant signals to a control system so that a pilot may be able to monitor the bleed duct air system from the cockpit.
During aircraft maintenance, it is necessary to test these sensors and circuit connections in order to determine whether the sensors are in good working order. Conventional methods of testing the sensors require removing the control system from its location in an electronics bay near the cockpit and attaching testing devices directly to the aircraft wiring at a rear interface of the control system in order to form a connection between the testing devices and the sensors. The testing devices are required to send alternating current through the sensors, since direct current can destroy the sensors. Such testing may therefore be performed when a suitable testing device is available at the location of the aircraft, which is generally infrequently due to the costs of such testing devices.